Run mobile apps in a visible simulator or emulator with once run --visible

You can now opt in to visible mobile runs by passing --visible to once run (and to the agent run tool). For Apple app targets, Once opens the Simulator before installing and launching the app. For Android binary targets that declare an emulator_device, Once starts that Android Virtual Device, waits for it to come online, then installs the app and launches the activity on the emulator. Existing headless once run behavior is unchanged unless you pass --visible.